Revealing carbocations in highly asynchronous concerted reactions: The ene-type reaction between dithiocarboxylic acids and alkenes

Chemoselective Oxidation of Isoxazolidines with Ruthenium Tetroxide: A Successful Intertwining of Combined Theoretical and Experimental Data

The direct oxidation reaction of isoxazolidines plays an important role in organic chemistry, leading to the synthesis of biologically active compounds. In this paper, we report a computational mechanistic study of RuO₄-catalyzed oxidation of differently N-substituted isoxazolidines 1a–c. Attention was focused on the endo/exo oxidation selectivity. For all the investigated compounds, the exo attack is preferred to the endo one, showing exo percentages growing in parallel with the stability order of transient carbocations found along the reaction pathway. The study has been supported by experimental data that nicely confirm the modeling results.

Chiral N-Triflylphosphoramide-Catalyzed Asymmetric Hydroamination of Unactivated Alkenes: A Hetero-Ene Reaction Mechanism

A highly enantioselective intramolecular hydroamination reaction catalyzed by chiral N-triflylphosphoramide (NTPA) that covers an exceptionally broad substrate scope of isolated unactivated alkenes was recently reported by some of us. Herein...

Alkene Epoxidations Mediated by Mn-Salen Macrocyclic Catalysts

Three new chiral Mn macrocycle catalysts containing 20 or 40 atoms in the macrocycle were synthetized and tested in the enantioselective epoxidation of cis-β-ethyl-styrene and 1,2-dihydronathalene. The effect of the presence of a binaphtol (BINOL) compound in the catalyst backbone has been evaluated, including by Density Functional Theory (DFT) calculations.

Functionalized polyhedral oligosilsesquioxane (POSS) based composites for bone tissue engineering: synthesis, computational and biological studies

Functionalized polyhedral oligosilsesquioxanes (POSS) containing an isoxazolidine nucleus have been synthesized by microwave assisted 1,3-dipolar cycloaddition of N-methyl-C-alkoxycarbonyl nitrone 1 with POSS containing olefin moieties. The results of cycloaddition processes were rationalized by computational studies at the DFT level. The covalent conjugation of chitosan with the cycloadduct 3a leads to composite material CS-POSS 7 which was gelified using genipin as cross linking agent. The suitability of the system for bone tissue engineering purposes was evaluated by in vitro drug release studies using ketoprofen as a model drug and cytotoxicity assays performed on human fetal osteoblastic cells. The preliminary biological tests showed the lack of cytotoxicity of the hybrid material and suggest its potential role in bone tissue engineering applications.

1,2,4-Oxadiazole-5-ones as analogues of tamoxifen: synthesis and biological evaluation

A series of 2,3,4-triaryl-substituted 1,2,4-oxadiazole-5-ones have been prepared as fixed-ring analogues of tamoxifen (TAM), a drug inhibitor of Estradiol Receptor (ER) used in breast cancer therapy, by an efficient synthetic protocol based on a 1,3-dipolar cycloaddition of nitrones to isocyanates. Some of the newly synthesized compounds (14d-f, 14h and 14k) show a significant cytotoxic effect in a human breast cancer cell line (MCF-7) possessing IC50 values between 15.63 and 31.82 μM. In addition, compounds 14d-f, 14h and 14k are able to increase the p53 expression levels, activating also the apoptotic pathway. Molecular modeling studies of novel compounds performed on the crystal structure of ER reveal the presence of strong hydrophobic interactions with the aromatic rings of the ligands similar to TAM. These data suggest that 1,2,4-oxadiazole-5-ones can be considered analogues of TAM, and that their anticancer activity might be partially due to ER inhibition.

Supramolecular recognition of phosphocholine by an enzyme-like cavitand receptor

The first example of supramolecular recognition of phosphocholine by a cavitand receptor has been reported here. The chemical structure of the receptor has been optimized by DFT calculations. The recognition mechanism is based on a "multi-topic approach", which leads to highly efficient (K value up to 10⁷ M^-1), selective and sensitive (ppb level) sensing of phosphocholine. The recognition mechanism proposed here is similar to those exploited by Nature, and paves the way for the realization of new sensors with important applications in medicine and security fields.

Transient and intermediate carbocations in ruthenium tetroxide oxidation of saturated rings

The ruthenium tetroxide-mediated oxidation of cyclopentane, tetrahydrofuran, tetrahydrothiophene and N-substituted pyrrolidines has been studied computationally by DFT and topological (analysis of the electron localization function, ELF) methods. In agreement with experimental observations and previous DFT calculations, the rate-limiting step of the reaction takes place through a highly asynchronous (3 + 2) concerted cycloaddition through a single transition structure (one kinetic step). The ELF analysis identifies the reaction as a typical one-step-two-stages process and corroborates the existence of a transient carbocation. In the case of pyrrolidines, the carbocation is completely stabilized as an energy minimum in the form of an iminium ion and the reaction takes place in two steps.